These Crutches can be made from regular Crutches, and a section of Aluminium Tube.
You can make a pair of these in half an hour.
I hope to make a more step-by-stepish Instructable, soon, with the help of some Fab-Lab... ;)
You just need a Tube Cutting tool, a Riveter, an extra Aluminium Tube, a pair of rivets, and a rubber band, or whatever to keep the thing together, when folded.
Step 1: How it's made
This is all you need to make a pair of fold-able Crutches that are affordable, and you can trust, since this uses the same set-up as the height regulation, two holes in witch a pair of holding pins with a spring will snap onto.
Not shown above is the separate tube section, that is there, but already riveted.
Step 2: Folded
A normal height-adjusted Crutch is made of a telescopic set of 2 Aluminium tubes where the thinner fits into the larger, the thinner tube has just 2 holes, and a spring with 2 pins snapped into those holes.
When the pins are fit into the larger tube's series of pairs of holes, the set becomes a solid crutch of a certain height.
So I use that same system to separate the Crutch in 2, and then, re-assemble the Crutch.
Here's the thing, folded.
The 2 parts of the Folding Crutch separate above the height adjustment holes, and snap into either the top pair of holes, or an extra pair of holes. an extra spring-and-pins piece is plugged into a new section of thinner tube, and that section is riveted into the larger tube.
Step 3: Snapped
To use the Crutches, just plug the thing together, the pins will snap onto the holes, and that's that!